An example of a transmitter or receiver is a so-called radio frequency identification (RFID) transponder used, for example, as an RFID tag or label. The transponder comprises a substrate, a receiver/transmitter circuit, and at least one conductive loop used as an antenna. The transponder receives queries from a base station and responds to them. The queries are transmitted by a transmission signal with a certain frequency, for example around 850 MHz to 960 MHz. The conductive loop of the transponder is the antenna that receives or transmits a transmission signal. The inductance of the conductive loop and an input or driving capacitance of the receiver/transmitter circuit form an LC-resonance circuit which is usually tuned to the frequency of the transmission signal through the choice of an appropriate conductive loop.
The integrated circuit and the conductive loop are normally arranged on a substrate, such as paper or an appropriate plastic sheet. Different materials for the substrate and different materials around the transponder in use may have different dielectric values, affecting the tuning of the antenna of the transponder negatively.
U.S. Pat. No. 6,028,564 discloses a receiver, specifically an RFID tag, comprising an antenna used as a voltage and power source designed to operate with an arbitrary load or front end. The antenna has an antenna section which comprises at least one element and at least one antenna terminal, and at least one loading bar placed adjacent to the elements at a spacing distance. The real part of the antenna input impedance is changed through adjustment of the load bar length, width, or spacing distance and by the number of loading bars.